1. Field of Invention
The present invention relates to dye lasers and, more particularly, is directed towards new lasing media for use in dye lasers.
2. Description of the Prior Art
Among the different kinds of lasers, dye lasers are unique by virtue of their relatively broad tuning range, which can exceed 50 nanometers with a single dye. By using different dyes in a single laser instrument it is possible to cover a broad, continuous range from the ultraviolet to the near infrared regions.
One present disadvantage of most dyes used in lasing media is the relatively short useful dye lifetime, which requires frequent replacement of the dye. At current laser dye prices the cost of dye during the useful lifetime of a dye laser instrument can greatly exceed the cost of the instrument itself.
Another difficulty with most laser dyes is that they require solvents having relatively poor thermo-optical properties compared to water, which cause a degradation of the laser performance of the dyes, especially at high energy loadings.
Accordingly, there is a need for efficient laser dyes with a high output-to-cost ratio, and there is also a need for laser dyes which can perform efficiently when dissolved in water.
One object of this invention is to provide new, efficient, inexpensive dye lasers.
Another object of this invention is to provide new laser dyes which can lase efficiently in aqueous solutions.
As used herein, the term "dye" refers to a molecular entity which can absorb electromagnetic radiation of wavelength longer than 300 nanometers (nm). The term "fluorescent dye" refers to a dye which can be made to emit light from its lowest excited singlet level, and the term "fluorogenic dye" refers to a dye which can be easily converted into a fluorescent dye by a simple chemical step like, for instance, the attachment of a metal cation.
While the processes which result in dye laser action are essentially understood, such understanding is not sufficient to enable a scientist to predict the laser parameters of any given dye from the knowledge of its molecular structure, fluorescence emission spectrum, electronic transition probability and fluorescence quantum efficiency. While a high fluorescence quantum efficiency and a high electronic transition probability are generally required for efficient laser action, many dyes meeting these two requirements do not lase, or lase too inefficiently to be useful. For instance the dye Rubrene has a fluorescence quantum efficiency of nearly unity in a number of solvents, but it does not lase in any of them. Often a dye with a high fluorscence efficiency, which is structurally similar to an efficient laser dye, fails to exhibit laser action, or lases inefficiently. For instance, the Al.sup.3+ chelate of the pentahydroxyflavone dye Quercetin does not lase, in contrast to the Al.sup.3+ chelate of the structurally very similar pentahydroxy flavone dye Morin.
It follows, then, that while the search for new, efficient laser dyes has to be guided by basic physical principles, a substantial amount of trial and error work is also required.